A173891 Numbers n such that the n-th noncomposite number plus the (n+2)nd noncomposite number is an even semiprime.

1, 3, 16, 37, 40, 47, 55, 56, 74, 103, 108, 111, 119, 130, 161, 165, 185, 188, 195, 200, 219, 240, 272, 273, 292, 340, 359, 388, 420, 427, 465, 466, 509, 521, 554, 600, 606, 622, 630, 634, 668, 683, 684, 703, 710, 711, 734, 762, 792, 814, 822, 823, 830, 831

Offset

1,2

Comments

Numbers n such that (A008578(n) + A008578(n+2))/2 is prime.

Is this the same as A173390? - R. J. Mathar, Jul 22 2010

Links

Table of n, a(n) for n=1..54.

Formula

prime(a(n+1)-1) = n-th balanced prime.

Maple

A008578 := proc(n) if n = 1 then 1; else ithprime(n-1) ; end if; end proc: for n from 1 to 1000 do sp := A008578(n)+A008578(n+2) ; if type(sp, 'even') and numtheory[bigomega](sp) = 2 then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Apr 25 2010

Crossrefs

Cf. A006562, A008578, A100484.

Sequence in context: A031302 A217130 A173390 * A066875 A294419 A196596

Adjacent sequences: A173888 A173889 A173890 * A173892 A173893 A173894

Keyword

nonn

Author

Juri-Stepan Gerasimov, Mar 01 2010

Extensions

All but one value shifted by 1, and missing values (40, 634, 762) inserted, by R. J. Mathar, Apr 25 2010

Status

approved